How does creativity express itself? How do we recognize it?
I think it helps to think of the word 'create' very literally here to understand it. It essentially means to manifest something into being. An idea starts as nothing, then it's a spark, then it's a fire. With this in mind, something is more creative when it seems to come out of nowhere as opposed to making a modification on something already familiar.
We recognize it in the sense that it seems oddly correct or familiar, but we never were able to connect the dots in such a complete way. This is why the most creative can seem foreign or threatening and the less creative seem pedestrian or obvious.
*edit* So, I think creativity is a more specific concept than most people think. It is the part of the mind that connects the dots, as distinct from deciphering. Creativity brings things into being, deciphering explains those things. Both abilities are valuable. I think we're lazy with our words, so I wanted to point that out.
I disagree with the general idea that asocial oddballs are all the geniuses or that geniuses are loners. This is a cliche. I understand what you're saying, but I think this notion has become overstated over the years. I definitely think setting and nation have something to do with it. Geniuses seem to cluster to a certain extent - Greek Philosophy, Italian Baroque, French PostModernism, Norwegian Black Metal.